20 WCM Words

Spring, 2017 - VOL. 22, NO. 2 Evan L. Heller, Editor/Publisher Steve DiRienzo, WCM/Contributor Ingrid Amberger, Webmistress FEATURES 2 Ten Neat Clouds By Evan L. Heller 10 Become a Weather-Ready Nation Ambassador! By Christina Speciale 12 Interested in CoCoRaHS? By Jennifer Vogt Miller DEPARTMENTS 14 Spring 2017 Spotter Training Sessions 16 ALBANY SEASONAL CLIMATE SUMMARY 18 Tom Wasula’s WEATHER WORD FIND 19 From the Editor’s Desk 20 WCM Words Northeastern StormBuster is a semiannual publication of the National Weather Service Forecast Office in Albany, New York, serving the weather spotter, emergency manager, cooperative observer, ham radio, scientific and academic communities, and weather enthusiasts, all of whom share a special interest or expertise in the fields of meteorology, hydrology and/or climatology. Non-Federal entities wishing to reproduce content contained herein must credit the National Weather Service Forecast Office at Albany and any applicable authorship as the source. 1 TEN NEAT CLOUDS Evan L. Heller Meteorologist, NWS Albany There exist a number of cloud types based on genera as classified in the International Cloud Atlas. Each of these can also be sub-classified into one of several possible species. These can further be broken down into one of several varieties, which, in turn, can be further classified with supplementary features. This results in hundreds of different possibilities for cloud types, which can be quite a thrill for cloud enthusiasts. We will take a look at 10 of the rarer and more interesting clouds you may or may not have come across. A. CLOUDS INDICATING TURBULENCE 1. Altocumulus castellanus – These are a species of mid-level clouds occurring from about 6,500 to 16,500 feet in altitude. They are very white and may take on the appearance of small battlements or jellyfish, usually containing both wispy and puffy parts. They are associated with moderate turbulence and a high mid-latitude lapse rate, and when these clouds are observed during the morning hours, they are an indication of high instability and a good likelihood of late afternoon and early evening thunderstorms. When seen in the late afternoon, however, they foretell of a fair weather night. While not a particularly rare cloud, they are more commonly seen in the Northeast during the warmer months. Altocumulus castellanus over Sacramento, California on the morning of August 12, 2014. Photo courtesy of NWS Sacramento, CA. 2 2. Kelvin-Helmholtz wave clouds – Also known as “fluctus” or “billow” clouds, these are a special variety of cloud, occurring with Cirrus, Altocumulus, Stratocumulus, Stratus, and occasionally Cumulus, and are most often associated with mountainous terrain. When seen, they typically stick around for only a few minutes, making them especially rare to see. This is a cloud that occasionally occurs over the Adirondacks, and is the result of two layers of winds traveling at sharply different velocities caused by the effect of friction by the terrain on the lower layer. This results in the formation of turbulent eddies, and the typical vertical swirl pattern seen in rows of these clouds. They are a fascinating sight. Kelvin-Helmholtz Wave Clouds. Photo Courtesy of the National Center for Atmospheric Research (NCAR). 3. Lenticular clouds – Often referred to as “mountain wave clouds” or “standing lenticular” (SL), these bright, stand-out clouds can be a species of: low-level Stratocumulus (SCSL), when they are also known as rotor clouds, or; high-level cirrocumulus clouds (CCSL). But in the Northeast, they are most often associated with mid-level altocumulus (altocumulus lenticularis, or ACSL). Their appearance can vary from ‘subtle’ to ‘dramatic’, the former of which is the one most observed in our neck of the woods, and the latter of which is usually reserved for more mountainous regions. Lenticular clouds form when wind encounters an obstruction, most often a mountain, and is forced into strong upflow, eventually condensing into clouds near the cold mountaintop. It appears to remain stationary for long durations, but is actually being subject to rapid changes in appearance due to strong shear. The size and overall dimension of a cloud is dependent upon the wind speed and the size of the obstruction. 3 Lenticular clouds in less mountainous regions tend to be more subtle, have a shorter lifespan, and can completely change appearance in the matter of just a minute or two. Aircraft avoid these regions because of the turbulent eddies that form within the cloud region. Due to the shape of these clouds, they are often mistaken for UFOs. Lenticular Rotor Cloud (SCSL) over Dublin, Ireland. Photo courtesy of Omnisource5. Lenticular altocumulus (ACSL) of duplicatus variety near Albuquerque, New Mexico on December 21, 2010. Note the multiple layers. Photo courtesy of Ethan Nelson (Source: NWS Albuquerque, NM). 4 4. Mammatus clouds – The “big mamma” of clouds, this is a species of cloud associated with several types of low-, mid- and upper-level clouds. Most of the time occurring in conjunction with thunderstorms, these dramatic bubbly- looking dark clouds result from the broad sinking of air through the cloud base, usually behind departing anvil thunderstorms. Contrary to popular belief, these clouds are almost never directly associated with tornadoes, and actually develop the vast majority of the time on the back side of a thunderstorm or cumulonimbus cloud, and are an indication of rapid stabilization of the atmosphere. These clouds can appear in one of many shades of gray, brown, green, blue, or even red. Mammatus clouds. Photo courtesy of NOAA. B. MUSHROOM CLOUDS These are the same clouds as produced by the atomic bomb, but are more commonly produced from volcanic eruptions, and are not classified as a genera of cloud as they are vertically-induced special clouds existing through a deep column. The condensation is the result of super-hot air from the volcano driven miles high into the super-cold upper levels of the atmosphere, where these clouds are typically driven globally and can persist for days or longer. Bigger volcanic eruptions have resulted in short-term global cooling; the 1815 eruption of Mount Tambora in the 5 Dutch East Indies is an extreme example that produced the “Year Without a Summer” in 1816, which, as it was, occurred during a period called ‘the little ice age”. In North America, food shortages, and snow in July were some of the repercussions of this eruption due to the massive cloud shield that obstructed the insolation needed to produce normal summer warmth. Mushroom clouds can be produced on an even smaller scale, such as with large localized fires or explosions, whether natural or man-made. Mushroom clouds often have a thunderstorm-like anvil where the air at the top disperses high up in the atmosphere. Lightning may also be produced. Also like a thunderstorm, there tends to be debris fallout; but this is from the solid particulate matter associated with the eruption or explosion, rather than from water-derived rain or hail. As one can see in the image below, mushroom clouds can spread out at various altitudes, producing other cloud types. Ascending cloud from Redoubt Volcano, Alaska, from an eruption on April 21, 1990. The mushroom-shaped plume rose from avalanches of hot pyroclastic flows that cascaded down the north flank of the volcano. Photo courtesy of The U.S. Geological Survey. C. SPECIAL UPPER-ATMOSPHERIC CLOUDS 1. Nacreous clouds– Also known as “polar stratospheric cloud (PSC)” or “mother- of-pearl”, this rare cloud comes in two types. All typically portray iridescence. The first of these is broken down into three sub-types: type 1a contains large, irregular solid particles of nitric acid trihydrate (HNO3·3H2O); type 1b contains small supercooled liquid spheres of sulfuric acid (H2SO4) mixed with water, and; type 1c contains a mix of water-rich, solid nitric acid particles (not chemically bound with the water as in type 1a). Type 2 is more straight-forward, and consists of only water ice. This is probably the most common type. Nacreous 6 clouds occur at altitudes between 49,000 and 82,000 feet, just above the level of the highest cirrus clouds, and are best visible during civil twilight, or several hours after sunset, and mainly in winter. They are mostly limited to Scandinavia, Alaska and northern Canada, but can also form with mountain wave clouds (which they may somewhat resemble) at lower latitudes, although this is rare. Type 2 nacreous cloud, brightly lit above darker tropospheric clouds around sunset. Photo courtesy of Mark R. Schoeberl, NASA GSFC. 2. Noctilucent clouds– Made up entirely of ice crystals, these highest of all clouds can be observed throughout the night because they exist way up in the upper atmosphere at altitudes of typically 47 to 53 miles, where diffuse sunlight reflects off the ice particles deep into the night. These clouds are as rare as the existence of ice particles at these altitudes that make them up. They bear a resemblance to the soft look of cirrus, and the color is generally white to pale blue, but may also tend toward red or green. Usually seen at latitudes from 50° to 65° in the Northern Hemisphere, they have very rarely been seen at even lower latitudes. They are a sight to behold! Sign up for a spring session. Find your location. Listings beginning on page 13. 7 Noctilucent clouds over Stockholm, Sweden, July 12, 2014. Photo courtesy of Kevin Cho. D. ARCUS CLOUDS: DIRECTLY RELATED TO THUNDERSTORMS 1. Roll clouds- This first of the two main types of arcus clouds is a low, horizontal tube-shaped cloud associated with a thunderstorm gust front, or cold front along a line of thunderstorms. It forms as the result of cool, sinking air at the leading edge of the front undercutting and lifting the warm air being drawn into the storm’s updraft, which condenses and rolls with the shear of the winds.

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